The present invention relates generally to gas turbine engines, and, more specifically, to stator vanes therein.
In an aircraft gas turbine engine having a multi-stage fan assembly, stator vanes adjoin corresponding rotor blades for compressing air as it flows axially therethrough, with the compressed fan air being discharged from the engine for powering an aircraft in flight. In one conventional design, individual stator vanes have radially inner and outer platforms, each of which includes a respective pair of outer and inner hooks. The outer hooks support the vanes to a corresponding pair of outer rails extending circumferentially around an outer casing. The outer casing is typically split in two 180.degree. halves, with the individual stator vanes being installed into each half by circumferentially sliding the outer hooks within the cooperating outer rails until each casing half is filled except for one remaining stator vane.
Since aerodynamic force encountered during operation of the fan creates a circumferential component of force, one specially configured locking vane is typically provided in each casing half to prevent circumferential rotation of all the vanes during operation. Accordingly, each casing half typically includes an axial recess or slot therein adjacent to the axial splitline, in which is disposed an anti-rotation key. The outer platforms of the locking vane and adjacent standard vane are correspondingly notched at adjoining sides thereof for accommodating the key, and against which the locking vane outer platform circumferentially abuts for preventing rotation during operation.
Since the adjoining outer platforms require complementary notches for receiving a portion of the key, the corresponding bending strength of the platforms is reduced. The circumferential component of the aerodynamic forces developed on the vanes during operation is reacted through the outer platforms and into the outer casing. The decreased bending strength significantly increases reaction bending stresses in the outer platforms which becomes a more significant concern for high solidity vanes wherein a greater number of circumferentially adjoining vanes must share a limited circumferential extent in the outer casing in which the aerodynamic forces are reacted. Since the platform end-notches are required for receiving the anti-rotation keys at two locations, all of the standard vane outer platforms are similarly notched on both sides for reducing unique parts count and reducing overall weight of the stator, and because the outer platform design is only as strong as the weakest platform, which is found at the locking vanes.
Although all the outer platforms are therefore identical, the locking vanes at the casing splitline are nevertheless unique and otherwise configured differently than the remaining standard vanes for effecting anti-rotation of the inner shrouds which are conventionally mounted on the inner platform hooks. The inner shrouds are typically arcuate segments which circumferentially adjoin each other to collectively form a ring, with each inner shroud having a corresponding pair of rails which engage the corresponding inner hooks of the vanes. After the standard vanes are initially assembled into each casing half during assembly, the individual inner shrouds are installed circumferentially along the corresponding inner hooks. The inner shrouds are typically identical in configuration and in circumferential length, except for one inner shroud in each casing half which is notched at one circumferential end in the corresponding rails thereof to define a special locking shroud that receives the specially configured inner hooks of corresponding locking vanes at the casing splitline position.
The inner hooks of the locking vanes are typically identical to those of the standard vanes except that they include integral dams or filled-in portions at one circumferential end thereof. The dams are radially aligned with the corresponding rails of the inner shrouds to prevent relative circumferential movement therebetween for thereby preventing circumferential rotation of the inner shrouds during operation of the engine. However, the locking shroud end notches are sized for receiving the locking vane dams. In this way, the standard inner shrouds are assembled to the inner hooks of the vanes in each casing half during assembly. The locking shroud is then similarly assembled to the inner hooks, leaving the notches thereof positioned adjacent to the casing splitline. The locking vane is then assembled with its corresponding anti-rotation key between the outer casing and the outer platform, and with the dams of the inner hooks being positioned within the notches provided in the locking shroud. The two casing halves are then assembled and bolted together to complete the assembly.
Omission of the anti-rotation features at the outer casing or inner shrouds is of course undesirable. Since the anti-rotation key is trapped between the outer platforms and the casing, it is hidden from view and omission thereof is not discernable after assembly. If a standard vane is assembled instead of the locking vane, both the vanes and inner shrouds will no longer be restrained from circumferential movement. Accordingly, it is desired to have an improved stator assembly which prevents incomplete assembly or misassembly during the assembly process.